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Common Cookware Cross-contamination with Gluten Post Customary Sanitation Study

Journal of Gluten Sensitivity Autumn 2012 Issue

Image: CC--Nicki Dugan Pogue 09/22/2017 - Misdiagnosed my sophomore/ junior year of High School, 3 years ago, with celiac disease, I became obsessed with the science of this ailment and how it was supposedly affecting me. I was shocked by how little is known about this autoimmune disease and the many gaps in research done on it. One such gap is that of cross-contamination in the household, where it is likely to have a daily impact on those following gluten-free diets. Because of this, I decided to help fill this gap in scientific knowledge with a manageable project based on cross-contamination in the home, asking whether one can share common kitchen cookware that is used with gluten containing foods, or if people, to help maintain a gluten-free diet, need designated ones for their food preparation.

Either way that this research played out would be beneficial to the gluten-free community. For example, some families with members on gluten-free diets will spend a lot of money to buy all new ‘gluten-free' designated cookware and utensils to help minimize cross-contamination. Part of the relevancy of this project is economical, as designated cookware can be very costly. Despite the cost, other factors affect the value of this research, including the impracticality of having a double set of kitchen appliances, which would be very bulky and impractical for those with limited space. Another factor that influences the significance of this project is beyond one's home; celiac disease brings a lot of social stress. By assuring there is limited or no cross-contamination from common kitchen appliances after customary washing, these individuals would be able to have some confidence when eating at friends' or families' homes. On the other end, if this research shows that there is cross-contamination with shared supplies it will highlight the need for dedicated ones to maintain a strict gluten-free diet. Just because a gluten-free recipe is used, a given dish may not be genuinely gluten free if there is contamination from cookware.

Hazards and Concerns
To fully understand the hazards of gluten contamination, a few things must first be established: What is gluten? Who is it harmful to? How and to what extent must it be avoided? How does cross-contamination occur?

What is Gluten?
The United States Food and Drug Association (FDA) have been trying to define "gluten" for years. The current proposed definition is, "the proteins that naturally occur in a ‘prohibited grain' that may cause adverse health effects in persons with celiac disease."(1) These prohibited grains are any species belonging to triticum, hordeum and secale or more commonly called respectively: wheat, barley, and rye, though other prohibited grains exist as hybrids of any of the three.(2) That being said, not all proteins in these three types of grains are toxic to those with celiac disease as there are two parts to glutens: prolamins, the immunotoxic ones, and glutenins, the safe ones.(3) The prolamins in the three main prohibited grains, wheat, barley, and rye, are gliadin, hordein, and secalin.(4)

Who Does Gluten Harm?
Gluten is toxic to certain individuals with celiac disease, an autoimmune disease that also goes by the names of: coeliac disease, celiac sprue, nontropical sprue, and gluten-sensitive enteropathy.(5) A Thomson Healthcare Company study estimated that up to 1.5 Million Americans, or one in 133 people, have celiac disease, though other individuals avoid gluten as well, such as those with gluten intolerance, or other ailments where a gluten-free diet is believed to lessen their symptoms.(6) This strict abstention from gluten is because celiac disease cannot be cured, or mediated with medication as yet. The only way to help those affected is by following this strict diet.

How and to What Extent Must it be Avoided?
Foods that contain wheat, rye, and barley, or any hybrid of these grains contain gluten. Gluten is a very common protein in foods, whether from bread, or as an additive to provide a thicker texture, such as in soups. This versatility makes processed foods, in the eyes of those on gluten-free (GF) diets, something to be wary of. Because of this caution, companies want their products to be certified GF, which according to the FDA calls for

Despite current unknowns regarding contamination, a strict gluten-free diet must exclude all foods that contain gluten and minimize cross-contamination. This means from eating out, to staying in, gluten must be avoided. Topical products where gluten is added, such as in some lotions or body washes, should also be avoided. Despite the widespread use of gluten there are gluten-free grains and foods, such as beans, rice, millet, corn, amaranth, and soy.

How Does Cross-contamination Occur?
Cross-contamination is a term usually directed toward accidental spread of bacteria due to not cooking food, washing hands or materials. However, in this article it refers to the accidental transfer or content of gluten, the protein that is toxic to those with celiac disease.

In my personal experience and research on celiac forums, when a member of a family goes gluten-free the family will most likely continue eating a regular diet. In addition, as the average time it takes to be diagnosed from the first onset of symptoms is 10 years in the United States, these families have kitchen supplies that they have been using with gluten.(8) With little public knowledge about celiac disease and going gluten-free, people tend to overlook cross-contamination. Theoretically, in the simple act of making a sandwich with GF bread there are many different ways for it to become contaminated. For example, from a shared jar of peanut butter or jelly with crumbs accidentally getting into it and then dipped out onto the GF bread, or crumbs on the surface it's prepared on sticking to the GF bread.

Research Investigation
The investigation of common kitchen appliances that are frequently exposed to gluten and cleaned by customary sanitation techniques calls for the conduction of an enzyme linked immunoassay (ELISA) test when using them to prepare gluten-free food. Various well used kitchen appliances, wood and plastic cutting boards, cast iron skillets, both seasoned and unseasoned, Teflon and aluminum pans, and ceramic and glass bowls were contaminated with gluten, using whole wheat flour slurry, and then washed by their standard cleaning technique, either scrubbing with hot soapy water, or wiping with a paper towel and water.

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Afterward a certified gluten-free substance, in this case millet flour, was added and let sit to allow adherence of any gluten remaining on the ‘cleaned' surface. Figure 1 illustrates the extraction solutions that were made from the samples and injected into the Microwell plates with the anti-body coating and the various washes of the ELISA test.

Then, the gliadin, if present, bound to the walls of the wells due to its antibody coating and the wells were washed to eliminate remaining parts in the well. Next, the enzyme Horseradish Peroxidase, or HRP enzyme, adheres post-injection to any gliadin present as an amplifier and is again washed to remove extra parts. Lastly, a 3,3', 5,5'-Tetramethylbenzidine, or TMB substrate was added which turns blue in the presence of a peroxidase, in this case the adhered HRP enzyme, which can only be there if there was gliadin to attach to. This color after a acid stop solution, which turns it yellow, is added is then assessed using a Microwell plate reader for its absorbency which, when compared with a standards curve made from known samples, by the company, will be used to determine the gluten content, in parts per million, of all the samples individually.

Intuition may lead one to think that well developed standard cleaning techniques for most appliances, and the difficulty in transferring proteins to a gluten-free medium from a surface that has been cleaned, will make gluten cross-contamination unlikely. However, due to factors such as porosity and oiliness, some surfaces may harbor gluten. Typically, far less rigorous cleaning techniques are used on the seasoned cast iron skillet and it is very porous and oily so the gluten proteins have a better chance of binding to it and then transferring to a gluten free medium. Given the test results of the ELISA test, this is mostly true. Despite the logic being the same, and it being the intuitive most likely candidate for cross-contamination a different appliance with the same sanitation technique proved to exceed the gluten parts per million limit where as the cast iron did not.

The only absorbency ratings from the samples that interpolated to be greater than the 20 ppm of gluten allowance were two extractions from the Teflon pan. All other ratings, including two other Teflon pan extractions, were below the limit.

Ninety-four percent of the sample extractions showed less than the 20 parts per million of gluten which is the threshold for something to be declared gluten-free. Teflon had half of its extractions above the limit, as such Teflon should be deemed cross-contaminated. However, the Teflon's other extraction samples had well below 20ppm. This could have been due to the sample's gluten free sample being rather large and thus only part of it could have gotten contaminated (positive cross-contamination) and other parts not (negative cross-contamination). All others samples were classified as gluten-free due to being below the 20ppm allowance.

In conclusion, the values of gluten cross-contamination, in ppm, were too small to hinder the integrity of the gluten-free medium in all but Teflon. Thus, to the extent of the experiment done, having tested only eight different kitchen appliances, with only two different sanitation techniques, common kitchen appliances that are frequently exposed to gluten, can be cleaned by customary methods and used to prepare gluten-free food with the exception of Teflon appliances.

This research project could be extended by more trials. For example, eight types of common kitchen appliance were used, but only one appliance was used to represent each type. More trials could be done within each type, using different brands, variations in extent of wear, etc. In addition, the only type of contaminant used was whole-wheat slurry. Other forms of contaminant should be tested as well, to show the universality of the cross-contamination, or lack thereof. This should include different gluten-containing substances, as well as some dry and some wet.

Unfortunately, this research question will have exceptions as the extent of washing and wear on an appliance is a more subjective issue. This means that even if it is found on a larger scale that certain appliances have been found to be safe for producing GF foods, it should still be avoided when possible for those with celiac disease as if not washed properly; it could go beyond the 20ppm allowance and be immunotoxic to these individuals.

Vested interest is always a concern with research, and thus it must be pointed out that no company or university holds any interest in this project and no help was given financially or academically, only that The University of Detroit Mercy allowed me to use their lab for the duration of the experiment and Microwell plate reader. In addition, both sides of the results would prove beneficial, so the data were not interpreted with a bias toward any desired result.

Eleanore Dara is a "rising scientist" and is an incoming biochemistry student on a Research Track Major at the University of Scranton in Pensnsylvania.


  1. "Questions and Answers on the Gluten-Free Labeling Proposed Rule." U S Food and Drug Administration. N.p., 23 Jan. 2007. Web. 31 Jan. 2011. 
  2. Ibid.
  3. Amaya-González, et al. "Amperometric Quantification of Gluten in Food Samples Using an ELISA Competitive Assay and Flow Injection Analysis." Electoanaylsis 23.1 (2010): 108+. Wiley Online Library. Web. 8 Mar. 2011.
  4. "What Is Gliadin? What Is Its Role In Gluten Sensitivity?." Gluten Free Around The World, Traditional Foods Make Eating an Adventure. N.p., n.d. Web. 25 Mar. 2012. 
  5. Snyder, Cara et al. "Celiac Disease Coeliac Disease, Celiac Sprue, Nontropical Sprue, Gluten-Sensitive Enteropathy." The National Center for Biotechnology Information. N.p., 3 June 2008. Web. 31 Jan. 2011.
  6. Cerrato, Paul L. "Gluten Intolerance: more common than thought. (Complementary Therapies Update)." RN 66.8 (2003): 23. General One File. Web. 28 Mar. 2011.
  7. "Questions and Answers on the Gluten-Free Labeling Proposed Rule." U S Food and Drug Administration. N.p., 23 Jan. 2007. Web. 31 Jan. 2011. 
  8. Adams, Scott. "USA - Average Time to Diagnosis = 10 Years -" Celiac Disease & Gluten-free Diet Information at Scott Adams, 26 July 1996. Web. 16 Feb. 2012. welcomes your comments below (registration is NOT required).

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6 Responses:

Dick Lunde
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said this on
22 Sep 2017 1:42:14 AM PST
Four years ago when I got diagnosed (biopsy confirmed), I stopped using a cast iron skillet that I'd used for various things, but most frequently for skillet-sizzled corn bread, using a recipe that contained wheat flour. But I thought there should be a way to clean the pan adequately. So eventually I filled it with water, added some dishwasher detergent and simmered that for an hour or so, which quite successfully stripped it of any seasoning. Then I went over it with an SOS pad and washed it with ordinary dish detergent (not dishwasher detergent as before). I re-seasoned it with multiple coats of flax seed oil, and have used it since for a modified, GF version of the cornbread a few times. I've noticed no symptoms of being glutened from eating that cornbread, and I do get glutened occasionally by other things (once by oyster sauce-- who knew it came in glutenous and GF versions?). So I believe the conventional wisdom that cast iron can't be cleaned up short of running it through the self-cleaning cycle of an oven is wrong. If I read this research correctly, I may not even have had to re-season the pan. And I think it's really great that someone is doing some research on cooking utensils. I suspect a lot of money has been wasted on new utensils when people have had to go gluten free. I've also wondered if gluten (or gliadin, or whatever form is retained by at least the teflon-coated utensils) is soluble in (or can be denatured by) any commonly available solvents or in/by water solutions of any common household chemicals. Another question of interest is how many times a gluten-contaminated vessel (such as the teflon-coated ones that were mentioned in the article) can contaminate something cooked in them if they're not further exposed to wheat (etc.).

Leslie Hutton
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said this on
25 Sep 2017 8:54:09 AM PST
I second Dick Lund's post. I stripped and re-seasoned my cast iron and stainless cookware when I had to go on a gluten free diet. I kept my wooden cutting board and the wooden spoons that my mother used. I've never noticed any problems using this cookware. My only question would be if it would be better to heat the metal pans during the gluten soak in order to replicate actual cooking conditions. Porosity and gluten absorbance may be altered at high temperatures used to fry chicken or stir fry noodles for example.

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said this on
25 Sep 2017 5:26:22 PM PST
Having dealt with my husband's celiac for years I have a few tips about cookware. I found these out by trial and error. Most mixing bowls, plates, utensils, etc are perfectly fine with normal washing as long as they are glass, ceramic or metal. Plastic holds gluten in crevices and should not be used. This is true of cutting boards, mixing bowls, etc. Never had a problem with cast iron skillets. Use 2 toasters. Jars of jam or peanut butter or anything dippable, I place a small bowl of it on the table for guests as they cannot remember not to put the knife back in, then I finish that portion myself and the jar remains GF. Any work on counter is on paper plates such as making sandwich. We use paper plates and cups a lot which also helps. Hope this helps people, I have been dealing with it a long time.

Joanna Davis
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said this on
25 Sep 2017 10:32:52 PM PST
As a 73 year old celiac who was not diagnosed until two years ago, I scoured all my cast iron skillets with non-iodized salt. This is the method I use to clean them each use, no detergent. I heat them each time before using them and have never experienced any issues. I am a very sensitive celiac. I sterilized all my baking pans and cookware in the dishwasher, did not throw anything away. I cleaned all my wooden spoons and cutting boards by scrubbing thoroughly and using boiling water to rinse, then dried them in the oven at 200 degrees. Also no problems. We do use separate toasters. I have double ovens, one strictly for gluten free baking. Separate tubs of margarine, peanut butter and jam jars. Only squeeze bottles for safe condiments in preparing foods. Pots and pans are washed in the dishwasher and sanitized. I store all left over foods in separate canning jars to avoid cross contamination in the refrigerator. I do not own Teflon cookware, never liked it. Thank you Elenore Dara for an insightful article. Keep up the good work. Going gluten free is a challenge on so many levels. I have given up eating out and I am a rabid label reader. I send emails all the time to companies that say gluten free and hide gluten in ingredients that are obviously made with gluten. Restaurants are the worst. I react to anything made with seaweed, i.e. MSG, carrageenan, alginate and agar as do many celiacs, these ingredients are in nut milks, dairy products of all kinds and baked goods. Carrageenan is a cheap emulsifier and the food industry loves it.

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said this on
26 Sep 2017 3:55:51 AM PST
It would be interesting to test used cookware that has a long history of being exposed to gluten and then used to cook gluten free food. This isn't something killed off by heat like a bacteria. The cooking process may bind gluten to a pot? Or perhaps release it? Also running items trough a common dish washer machine where lots of gluten exposure takes place, like in a Italian restaurant.

Mrs. Bright
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said this on
26 Sep 2017 5:20:24 AM PST
Love your article. It's been rough being the only gluten free person in the family. I'm finding out the hard way that seasonings can be contaminated even though the ingredient list does not show any Gluten ingredients. When my husband would season our food with Lawry's Seasoning I would get sick ever time. I finally called the company that makes Lawry's and asked them what ingredients are making my sick... well the guy tells me technically all the ingredients are Gluten Free BUT the machine they run the seasonings thru does contain wheat products. So I'm learning just because it doesn't list a Gluten items doesn't make it Gluten Free. I also learned this with Yellow Rice. Same problem. Anything that is processed may have Gluten UNLESS it has the GF listed on the label and has been approved a GF item.

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